Mystery mill - telescopic knee screw

I've today lifted the knee on my Mill of Mystery, an Italian 1960s Testa 2U (I've only heard of one other in captivity), as I'd stupidly run it up to the point where the screw and nut disengaged, damaging the top thread of the bronze nut - all came apart pretty easily, and when I lifted the nut housing out of the base I discovered about 12" of bronze male thread and that someone has been there before me... (Why can nobody trouble themselves to find a screwdriver that fits the slots??)



I assume that this (which is locked up solid) should also rotate, when the end of the (steel) elevating screw is reached, to give more elevation and that this is what has caused the screw to run out of the bronze nut...

End of the (inner, power-driven) elevating screw looks like there's room for a stop to butt against the bottom of the bronze screw's inner thread



And the damage done - looks like this has happened before and someone before me has "cleaned up" the top turn of the thread, I'll do the same as there's still nearly 2" of 5 TPI bronze Acme left in there



Both threads are the same 5 TPI, so there'll still be the same travel whether or not the nut rotates in its housing, but allowing the nut to screw in and out of the base should (I think) allow the full range of movement - anyone care to shoot me down in flames? I'll have to apply some BF&I to the nut to get it rotating in the housing, but it *should* simplify reassembly as I'll be able to screw the nut up to meet the elevating screw, attaching the stop to the bottom of the screw may be interesting though...

Thanks in advance for any suggestions, cautions, encouragement!

Dave H. (the other one)

It's a pretty common arrangement particularly on shapers - my 600 has it too and so does a small mill of mine. You're missing something there which will convince the nut to start rotating once the screw reached end of travel. I don't see any serious damage - normal stuff. I don't have the mill next to me but I have the shaper and I'll take a look to see how that thing is held together.

Thanks Alex,
I was thinking I could (once the nut's freed off) put a large washer/plate between the elevating screw and the "castellated" nut that's threaded on the end - I can't see any purpose for it other than to stop the screw threading through the nut *if* there's a stop sandwiched between 'em! The "bottom end" (far right in the pic) of the bronze nut has a floating thrust washer/bearing between it and the threaded collar (which has locating/locking grubscrews) which I assume is intended to bear against the housing when it reaches its limit screwing upwards into the housing (to the left in the pic).

The collar also has 5mm drillings, I guess for tommy bar/bars, I'll try to make up a Suitable Tool to try rotating the nut in its housing...

Thanks again,
Dave H. (the other one)

Hopefuldave said:

Thanks Alex,
I was thinking I could (once the nut's freed off) put a large washer/plate between the elevating screw and the "castellated" nut that's threaded on the end - I can't see any purpose for it other than to stop the screw threading through the nut *if* there's a stop sandwiched between 'em! The "bottom end" (far right in the pic) of the bronze nut has a floating thrust washer/bearing between it and the threaded collar (which has locating/locking grubscrews) which I assume is intended to bear against the housing when it reaches its limit screwing upwards into the housing (to the left in the pic).

The collar also has 5mm drillings, I guess for tommy bar/bars, I'll try to make up a Suitable Tool to try rotating the nut in its housing...

Thanks again,
Dave H. (the other one)

Click to expand...

Give me 10 mins.... I'll take a pic of a shaper screw.
Sorry, took pic but it doesn't want to upload it. The screw has a thin nut ( forgot the name ) which bumps into the first bronze nut and causes it to start rotating.

My Crafts***/A**** horizontal has a similar arrangement. At about 1/5 scale.....

That happens a lot on Bridgeport mills too. Someone removes the flat head screw that in between the column ways at the top not knowing that's a simple stop that a bolt on the back top face of the knee hits when it's raised to high. With that removed the screw feeds out of the elevating screw nut and buggers up the first thread and it won't turn back in. One has to dismantle that nut housing and mill,turn or grind out the bent over brass thread to get the screw to start again.

Your ID threads look sharp and thin in the one picture. If they are more then 1/2 gone I would make a new nut or mold one out of Moglice.

If your close to Hastings /Kent UK I will be there on Dec. 9th - 16 to teach a scraping class and I would love to see the machine some night after class.

Em..
perhaps this is silly .. but ..
a 2$ microswitch would easily stop any excess movement.

Is there a real *need* for the nut to rotate ?
Adding anything mechanical always adds errors into kinetic systems.

I think the arrangement is silly .. but may well be wrong.
Also Very Willing to learn better if so.

I would clean it, and locktite it into place.
I care nothing for past mechanical history unless its a museum - which I like.
The good part of locktite is its easily removed in 10 minutes with no damage.
A good hard collar is difficult, lots of work, and all sorts of risks in distortion etc.

A better devcon 4782 epoxy (iirc, the bearing stuff) is too permanent, but much more rigid by 10x or more.

All lathes and mills need rigidity as the nr 1 ingredient.
Every mechanical bit lessens rigidity by a power of n(axes).

I modify my machines at need.
1. From an ancient Bp getting a VFD,
2. to an AC motor on lathe getting replaced by a modern bigger brushless AC servo drive.
2- was the best thing I ever did - and better by 10x than I expected.

If the goal is working machines vs historical mechanical art, modern relatively cheap-and-cheerful electronics (2.5 kW AC brushless servo kit 1500€) and goops are outstanding.

Hopefuldave said:

I've today lifted the knee on my Mill of Mystery, an Italian 1960s Testa 2U (I've only heard of one other in captivity), as I'd stupidly run it up to the point where the screw and nut disengaged, damaging the top thread of the bronze nut - all came apart pretty easily, and when I lifted the nut housing out of the base I discovered about 12" of bronze male thread and that someone has been there before me... (Why can nobody trouble themselves to find a screwdriver that fits the slots??)

View attachment 212588

I assume that this (which is locked up solid) should also rotate, when the end of the (steel) elevating screw is reached, to give more elevation and that this is what has caused the screw to run out of the bronze nut...

End of the (inner, power-driven) elevating screw looks like there's room for a stop to butt against the bottom of the bronze screw's inner thread

View attachment 212589

And the damage done - looks like this has happened before and someone before me has "cleaned up" the top turn of the thread, I'll do the same as there's still nearly 2" of 5 TPI bronze Acme left in there

View attachment 212590

Both threads are the same 5 TPI, so there'll still be the same travel whether or not the nut rotates in its housing, but allowing the nut to screw in and out of the base should (I think) allow the full range of movement - anyone care to shoot me down in flames? I'll have to apply some BF&I to the nut to get it rotating in the housing, but it *should* simplify reassembly as I'll be able to screw the nut up to meet the elevating screw, attaching the stop to the bottom of the screw may be interesting though...

Thanks in advance for any suggestions, cautions, encouragement!

Dave H. (the other one)

Click to expand...

A slight correction: what I thought was a castellated nut, once I cleaned it a bit, turned out to be the end of the screw with a pair of key slots and the remains of a 10mm capscrew...

Plan now is the following stack on the end of the screw:
M10 x 25mm Capscrew through:
35mm dia Sturdy Washer;
20mm ID by 35mm OD thrust bearing;
20mm diameter by 12mm spacer with lugs matching the key slots in the screw;
finally screwing into the thread in the elevating screw itself.

On the principle that when the screw's extended and reaches its limit on the ID of the bronze nut/screw thing, the thrust bearing will prevent friction locking the two together - which I assume is what Boroughly Thuggered it in the first palce?

Struggling a bit getting the screw to move in the housing, heat and perpetrating oil, pair of BFI bars and not shifting (the BFI bars bent...) - last resort may be to cut away the paxolin? washer between bronze nut and the steel housing (second one down in the 3rd pic), as my assumption is that that's what's very firmly clamped between the two and preventing any movement - a bit big and awkward for the lathe though, so I may have to be incredibly careful with a hacksaw blade in the gap

Richard, it would be a pleasure to meet you, but I suspect I'll be either your side of the pond that week (NYC and Chicago) or visiting the fleshpots of Europe's financial centres (Frankfurt, Zurich, Stockholm, Madrid and Milan) for most of December - damn job gets in the way of all my fun! Although really it's not the job's fault, it's the customers leaving it to the last minute to comply with new EU regulations that kick in on the 3rd of January

If not, I'll definitely let you know, I'm about a 90 minute - 2 hour drive from Hastings though...

The bronze nut internal thread looks to be usable, at least for now, pre-ballsup winding it too far there wasn't that much backlash (the weight of the knee probably helps there, it's quite, er, Substantial with the feed motor and gearbox built into it and the Universal swivel, plus a four-foot table - nothing a 10-ton hydraulic jack can't lift though) - should it prove a problem I'll probably try the Evanut approach as Moglice isn't that easy to find in the UK?

Thanks all,
Dave H. (the other one)

hanermo said:

Em..
perhaps this is silly .. but ..
a 2$ microswitch would easily stop any excess movement.

Is there a real *need* for the nut to rotate ?

Click to expand...

Sometimes, yes. On some machines bringing the table at lowest point makes the screw go through the floor - a hole is usually provided. That arrangement cuts travel in half.

Hi Hanermo,

The reason the nut needs to rotate is to get the full vertical travel - otherwise it's limited to about 12"/300mm, so really restricts the work envelope, particularly as it doesn't have a quill (it has an universal tilt/swivel which is more use to me). The damage was probably done due to a missing stop dog for the power feed, replacement already fitted (and wondering if I can give it micrometer stops for individual jobs - although the planned DRO may come first and make 'em redundant).

At the moment Loctite would be unnecessary, the nut's firmly jammed in the housing! Bent two BFI bars already trying to shift it, but have some other things to try

I agree about museum vs usable machines, my Holbrook isn't at all original where its electrics are concerned - I've retained the 3-speed 415v motor, but hacked a VFD to give me 415 from 240 and added quite a lot of electronics/electrics to retain the Holbrook Experience, and it has ET's little brother's head with variable speed controls, tacho', motor current meter (although I've tried to make them look in keeping - vintage-style chicken-head knobs, WW2 "Admiralty Pattern" Bakelite meter - Nixie tubes are a lot of work to build a tacho' around, though, so red LED digits had to do...)
Gives me a better speed range, too, 2.2 - 2500 RPM and rapid braking etc., plus near-constant surface speed thanks to a slide potentiometer on the cross-slide (my attempt at what the Big Boys' have on their CNC machines....)

Dave H. (the other one)

Some progress - ground out about 60 degrees of the first turn of the bronze nut's thread (where would we be without our Dremelloids?), wound onto the elevating screw nicely, a bit more BFI and the nut started turning in the housing - refitted it apart from the thrust bearing (found the exact one in the Misc. Bearings drawer, I think I rescued it from the WBS a few months ago!), just need a few of the Right Washers, a M10 x 25 SHCS and a drop of Loctite and I can button it back up - at last!

Dave H. (the other one)

Hopefuldave said:

Some progress - ground out about 60 degrees of the first turn of the bronze nut's thread (where would we be without our Dremelloids?), wound onto the elevating screw nicely, a bit more BFI and the nut started turning in the housing - refitted it apart from the thrust bearing (found the exact one in the Misc. Bearings drawer, I think I rescued it from the WBS a few months ago!), just need a few of the Right Washers, a M10 x 25 SHCS and a drop of Loctite and I can button it back up - at last!

Dave H. (the other one)

Click to expand...

Good stuff ! Glad it worked out. Maybe one day you could post a pic or two of the machine - never heard of it and would like to see how it looks like.

Best pics I've got, I'm afraid - on the trailer on the way home and the EvilBay pic that piqued my interest


Dave H. (the other one)

That's very nice ! I don't think I've ever seen one. It's solid, plenty iron in it - it's going to take a decent cut. Good luck with your restoration !